1. Field of the Invention
The present invention relates to power tools, such as disk grinders, and in particular, to power tools having an air introduction device for cooling a motor.
2. Description of the Related Art
A disk grinder is known that has a cylindrical body casing and an electric motor disposed within the body casing as a drive source. The body casing is adapted to be grasped by an operator. An output shaft of the electric motor is supported by a front casing that is disposed on the front side of the body casing. The rotation of the output shaft is transmitted to a spindle. A circular rotary grinding disk is attached to the front portion of the spindle. A rear casing is disposed on the rear side of the body casing. An inlet opening for introducing air is formed in the rear casing. A cooling fan is attached to the output shaft of the motor, so that a flow of the air from the rear side to the front side of the body casing is produced as the fan rotates. Therefore, the air can cool components of the motor. More specifically, the external air enters the rear casing via the inlet opening, flows into the body casing, and is then discharged from an outlet opening formed in the front portion of the body casing.
Techniques for channelling air into the body casing are disclosed in Japanese Laid-Open Patent Publications Nos. 9-272073 and 2002-18745. In these publications, the inlet opening is formed in a side portion of the rear casing.
It has been also known to attach a net-like filter to the inlet opening for preventing dust in the air from entering into the body casing through the inlet opening. However, the filter may increase resistance against flow of the air through the inlet opening and thus causes reduction in the flow rate of the cooling air. A proposed solution is to provide a plurality of guide plates 52 with respective shielding plates 53 as shown in FIG. 4. In the arrangement shown in FIG. 4, a plurality of inlet openings 51 are formed in opposite sides of a rear casing 50. The guide plates 52 extend horizontally and inwardly from an inner wall of the rear casing 50 at positions adjacent to the inlet openings 51. The shielding plates 53 are formed by upwardly bending the innermost ends of the guide plates 52. With this configuration, the dust in the external air entering the inlet openings 51 may collide with the shielding plates 53, so that the dust can be separated from the flow of the air. Hence, it is possible to introduce the external air into the rear casing 50 without substantial increase in the flow resistance, and therefore, a sufficient flow rate of the air containing a small amount of dust can be ensured.
However, according to the arrangement shown in FIG. 4, because all the shielding plates 53 extend upward toward the upper region of the rear casing 50, the flow of the air entering the rear casing 50 from its left side and the flow of the air entering the rear casing 50 from its right side may collide with each other within the upper region of the rear casing 50. In addition, some of the dust may not be shielded by the shielding plates 53 but may enter the upper region of the rear casing 50 with the flow of the air entering from both right and left sides of the rear casing 50 as shown in FIG. 4. Therefore, the dust carried by the flow of the air entering from the right side of the rear casing 50 and the dust carried by the flow of the air entering from the left side of the rear casing 50 may collide with each other, so that the dust may aggregate within the upper region of the rear casing 50 as indicated by a region D.
In general, functional elements of the motor, such as a commutator and carbon brushes are disposed within or near the upper region of the rear casing 50. Therefore, if the amount of the aggregate dust within the upper region of the rear casing 50 increases, it is possible that the motor may malfunction because of the build-up of particulate.
Therefore, there has been a need for a power tool including an air introduction device that can introduce an external air into a casing without causing potential aggregation of dust within the casing.